1. Field of the Invention
The present invention relates to a copier, facsimile apparatus, printer or similar image forming apparatus. More particularly, the present invention relates to an image forming apparatus of the type including a revolver type developing unit rotatably mounted on an apparatus body and having a plurality of developing sections, and an intermediate image transfer body having an endless movable surface to which a toner image is transferred from an image carrier.
2. Discussion of the Background
It is a common practice with an image forming apparatus of the type described to rotate a developing unit to bring a desired developing section thereof to a developing position for development, then cause an intermediate image transfer body carrying a toner image transferred from an image carrier to run idle, and then transfer the toner image from the image transfer body to a recording medium. For example, when a thick sheet mode for forming a toner image on, e.g., a thick sheet or an OHP (OverHead Projector) sheet is selected, the above idle run of the intermediate image transfer body is effected in order to slow down the movement of the body for again determining the position of the same. Further, when toner images sequentially formed on the image carrier by the developing sections are transferred to the intermediate image transfer body one above the other, it is likely that the leading edge of, e.g., the toner image of a first color formed on the image transfer body moves away from a transfer position where the image carrier and image transfer body face each other before the developing section assigned to a second color arrives at the developing position. In such a case, too, the intermediate image transfer body is caused to run idle.
However, the problem with the conventional image forming apparatus is that when the developing unit is inadvertently rotated during the idle run of the intermediate image transfer body, toner deposited on the image carrier by the developing section moving past or brought to the developing position is apt to deposit on the toner image forming area of the image transfer body. Such toner cause band-like contamination (lateral color band in the case of a color image) extending in the lateral or widthwise direction of a recording medium.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 7-152218, 8-76590, 8-190258, 9-106152, and 11-174776.